1. Field of the Invention
This invention relates to a dc motor which is well suitably used to wind and rewind a film in a camera or a like apparatus and a controlling system for a dc motor.
2. Description of the Prior Art
Various dc motors which are driven by a voltage supplied thereto from a power source battery are already known. However, in such dc motors, reduction in voltage of the power source battery may sometimes result in delay of operation or halting of a mechanism which is connected to be driven by the dc motor.
Therefore, an improved arrangement has been proposed, for example, by a Japanese patent laid-open No. 60-194433, wherein a transmission mechanism for transmitting rotation of a motor to a driven mechanism includes, in order to use the driving force of the motor as effectively as possible, two gear trains whereby if the rotational speed of the motor decreases, the motor is temporarily rotated in the reverse direction to change over from the normal high torque gear train to the other lower torque gear train so that the driven mechanism may be driven at a low speed.
However, such conventional arrangements of the type mentioned requires two different gear trains as a transmission mechanism as well as a change-over mechanism for selectively using one of the two gear trains in order that a motor may be driven also at a low speed. Accordingly, it is a drawback of the conventional arrangements that they are complicated in mechanical construction and hence they may have a large overall size and be produced at a high production cost.